The present invention is directed to a new process for the large scale production of alkali metal alcoholates free from alcohol of crystallization which are soluble in inert solvents or mixtures of solvents.
The alkali and alkaline earth metal derivatives of alcohols, phenols and enols are of great significance as intermediates, reactants and catalysts in the synthesis of many organic compounds. A series of different processes are known for their productions (see Houben-Weyl Vol. VI.sub.2 (1963) pages 7 et seq.). In principle one of these processes consists of reacting the free alkali metal directly with the alcohol. This reaction takes place more or less vigorously according to the degree of dispersion of the alkali metal. With increasing chain length of the alcohol the reaction is slowed down, primary alcohols reacts most violently, tertiary alcohols the slowest. For example, the reaction speed of tert. butyl alcohol at room temperature is only about 1/65 that of methyl alcohol, that of tert. amyl alcohol only 1/175 (see S. Volpe and G. Tlustos, Annali di Chimica Vol. 62 pages 399-407 (1972).
Precisely the alkali metal derivatives of the last named alcohols, however, in recent times have found increasing interest as catalysts and condensation agents, since both tert. butylate and tert. amylate are particularly strong proton acceptors because of the very small acidity of the pertinent alcohols and the strongly sterically hindered alcohols set free in the reactions for the most part do not undergo side reactions. Since the alkali metal derivatives of the tertiary alcohols in crystal alcohol free form beside are partially well soluble in inert solvents and mixtures of solvents, these alcohols are particularly advantageously added in this form in many reactions.
For the production of alkali metal alcoholates free from alcohol of crystallization therefore for a long time there has been sought a simple large scale process. Mainly, the previously proposed processes are suited almost exclusively for preparations on a laboratory scale, be it because the products are produced with excess alcohol and thus must be freed from alcohol of crystallization by a time consuming and cumbersome operation or be it because the alcohols must be reacted with expensive and difficult to handle reagents such as sodium hydride or sodium amide (see Houben-Weyl, Vol. VI.sub.2 (1963) pages 11 et seq.).
Also the process of Lochmann, Coupen and Lim (see Collection Czechosl. Chem. Comm. Vol. 35 pages 733-736 (1970)) in which alkali derivatives are first separated as adducts of tetrahydrofuran and are obtained from these adducts in pure form by evaporation of the tetrahydrofuran is too cumbersome for the production of the alcoholates on a commercial scale.
For the direct production of alkali metal alcoholates of tertiary alcohols free from alcohol of crystallization in inert solvents or solvent mixtures there has recently been proposed a process in which the added metal is used in equimolar amounts or preferably in excess and in which the reaction is carried out in an inert solvent or solvent mixture under increased pressure at temperatures at which or above which the alcohol of crystallization is split off (see German Auslegeschrift No. 2,333,634). In this process, however, there are still needed undesirably long reaction times. Also, disadvantageous are the high reaction temperatures as well as the alkali metal excess required in this process which in the course of several reactions is enriched with impurities which lead to disturbances or to expensive purification operations.
It is also known to increase the reaction speed in the reaction of long chain primary alcohols by adding the alkali metal in a finely "atomized" condition. According to the previously described processes, however, there can be produced alkali metal derivatives of unbranched primary alcohols free from alcohol of crystallization if first there is formed an alkali metal dispersion in boiling hydrocarbons and after cooling this there is dropped in the calculated amount of the primary alcohol (see Houben-Weyl, Vol. VI.sub.2 (1963) page 8; Ethyl, British Pat. No. 727,923). However, according to this proposal it is not possible to employ secondary and tertiary alcohols as well as iso-alcohols and those with a branched chain in rapid reaction. The reactivity of the last named alcohols with alkali metals is so small that according to the known process industrially unusable long reaction times are required. If one tries to carry out the described process then in an expensive manner one must first produce a sodium dispersion in xylene in 30 minutes, which dispersion is added for this reaction only after cooling. However, even with a dispersion of 5.mu. particle size in reacting tertiary alcohols at room temperature no satisfactory reaction speeds are developed so that even at the sought reaction times of up to 30 minutes the added alcohol after a few minutes no longer reacts completely; the remaining unreacted alcohol then leads to the precipitation of alcohol of crystallization containing alcoholates. An increase of the reaction temperature up to the melting point of sodium likewise does not lead to the desired results because with increasing temperature the sodium metal increasingly softens and therefore with the still necessary reaction times of over 15 minutes the dispersion clots together after a few minutes.
Therefore, there must be tried other ways to produce the desired alcohol of crystallization free alkali metal alcoholates in an economical industrial process. The object of the present invention therefore was to develop a process for the production of these alcoholates soluble in inert solvents which does not have the described disadvantages, i.e., without excess of a reactant in economically usable reaction times and in a simple reaction of alkali metal with alcohol in an inert solvent or solvent mixture form the desired, previously difficult producible alcoholates.